Grading  Mitotic count (10 HPF*) Ki-67 index (**) G1 2 <2% G2 2-20 3-20% G3 >20 >20% *HPF: High Power Field, 2 mm2; based on at least 50 fields (at 40× magnification) in tumor areas with higher mitotic density (“hot spots”); **MIB1 antibody; % on 500-2000 cells in tumor areas with higher density.

Table 2: Definition of tumour grading for NETs of the digestive system according to WHO 2010 classification.